1. Field of the Invention
The present invention relates to a sound field measuring apparatus and a sound field measuring method which are useful for, in an audio system having a plurality of speakers, correcting output signals for the speakers.
2. Description of the Related Art
In a conventional audio system having a plurality of speakers, it is preferable that a reproduced sound image is localized at a predetermined position and the sound field is correctly reproduced. Therefore, it is required to correctly know the time of arrival from each of the speakers to the listener. Conventionally, an impulse signal is used as means for measuring the time of arrival.
The time of arrival is measured by using an impulse signal in the following manner. An impulse signal is output from a speaker. The signal is detected by a microphone disposed at a predetermined position (listening position), and an impulse response between the speaker and the microphone (listener) is calculated. In this specification, the time of arrival means a time period from a time when an impulse response is input, to that when an impulse response reaches the maximum peak value.
In the above-mentioned measuring method, however, it is difficult to correctly calculate the rising time of the speaker which indicates a response concentrated into a low-frequency region. When a speaker of a moderate response is used, the rising time cannot be correctly determined. Depending on conditions of installing the speaker and the like, a case where background noises or indirect sound components are larger than direct sound components may sometimes occur. In such a case, it is impossible to correctly perform the time measurement.
It is an object of the invention to provide a sound field measuring apparatus which can correctly determine the rising time of a speaker.
The sound field measuring apparatus of the invention comprises: a pulse signal generating section (11, and the like) for outputting a pulse signal to speakers (4a, 4b, . . . ); a pulse signal detecting section (6, and the like) disposed in an acoustic space (5) where the speakers (4a, 4b, . . . ) are placed and for detecting a pulse signal output from each of the speakers (4a, 4b, . . . ); a time detecting section (15) for detecting a time when the signal detected by the pulse signal detecting section (6, and the like) exceeds a predetermined threshold; and a calculating section (15) for calculating a time period from a time when the pulse signal is generated by the pulse signal generating section (11, and the like) to a time of detection by the time detecting section (15).
In the sound field measuring apparatus, the time when the signal detected by the pulse signal detecting section (6, and the like) exceeds the predetermined threshold is detected. Even in the case of a speaker of slow rising, such as a subwoofer, therefore, it is possible to detect a rising portion in which the amplitude is very low. Consequently, the rising time of the output of the speaker can be correctly detected. When the threshold is adequately set, the true rising time can be detected by capturing the first response, even under circumstances where background noises or indirect sound components have a large energy.
The other sound field measuring apparatus of the invention comprises: a pulse signal generating section (11, and the like) for outputting a pulse signal to speakers (4a, 4b, . . . ); a pulse signal detecting section (6, and the like) disposed in an acoustic space (5) where the speakers (4a, 4b, . . . ) are placed and for detecting a pulse signal output from each of the speakers (4a, 4b, . . . ); a rising emphasizing section (151) for performing a process of emphasizing rising of the signal detected by the pulse signal detecting section (6, and the like); a time detecting section (152) for detecting a time when the signal obtained from the rising emphasizing section (151) exceeds a predetermined threshold; and a calculating section (153) for calculating a time period from a time when the pulse signal is generated by the pulse signal generating section (11, and the like) to a time of detection by the time detecting section (152).
In the sound field measuring apparatus, the time when the signal detected by the pulse signal detecting section (6, and the like) exceeds the predetermined threshold is detected. Even in the case of a speaker of slow rising, such as a subwoofer, therefore, it is possible to detect a rising portion in which the amplitude is very low. Consequently, the rising time of the output of the speaker can be correctly detected. When the threshold is adequately set, the true rising time can be detected by capturing the first response, even under circumstances where background noises or indirect sound components have a large energy. Furthermore, the time when the signal which has undergone the process of emphasizing rising of the signal detected by the pulse signal detecting section (6, and the like) is detected. Even in the case of a speaker of slow rising, therefore, it is possible to detect a time in the vicinity o f the rising o f the speaker.
The pulse signal output from the pulse signal generating section (11, and the like) may be a signal in which a power is concentrated into a region that is lower in frequency than an impulse signal. In this case, the S/N ratio with respect to background noises in which the level of the low frequency region is usually low can be set to be larger, and hence the rising time of the speaker can be correctly detected even under circumstances where background noises are relatively large.
The pulse signal may be a signal which attenuates with the lapse of time after rising of the pulse signal, or the pulse signal may be an exponential pulse. Alternatively, the pulse signal may be a signal which is obtained by passing an impulse signal through a low-pass filter. The pulse signal may be output by actually passing an impulse signal through a low-pass filter, or a signal which is obtained by passing an impulse signal through a low-pass filter may be stored as data, and a signal which is produced on the basis of the data may be output.
The pulse signal output from the pulse signal generating section (11, and the like) may be a signal in which a power is concentrated into a region that is lower in frequency than an impulse signal, and the rising emphasizing section (151) may perform a process of substantially flattening a frequency characteristic of the signal input into the time detecting section (152).
In this case, since the frequency characteristic of the signal which is input into the time detecting section (152) is substantially flattened, it is possible to extract the true transmission characteristic, so that measurement can be performed at the same accuracy irrespective of the band used by the speaker.
The pulse signal may be an exponential pulse, and the rising emphasizing section (151) may perform a process of applying differential of first order to the signal detected by the pulse signal detecting section (6, and the like). In this case, in the process of emphasizing the high frequency region and linearizing phase delay between bands, the computational complexity in the rising emphasizing section (151) can be suppressed to a minimum level.
The apparatus may further comprise: the signal delaying section (1) for delaying an audio output signal which is output to the speaker; and a delay time setting section (13) for setting a delay time of the the signal delaying section (1) on the basis of the time calculated by the calculating section (153). In this case, the delay time of the the signal delaying section (1) can be set to a desired delay time in accordance with the time calculated by the calculating section (153), without requiring a cumbersome work.
The sound field measuring method of the invention comprises: a pulse signal generating process of outputting a pulse signal to speakers (4a, 4b, . . . ); a pulse signal detecting process, disposed in an acoustic space where the speakers (4a, 4b, . . . ) are placed, of detecting a pulse signal output from each of the speakers (4a, 4b, . . . ); a time detecting process of detecting a time when the signal detected by the pulse signal detecting process exceeds a predetermined threshold; and a calculating process of calculating a time period from a time when the pulse signal is generated by the pulse signal generating process to a time of detection by the time detecting process.
In the sound field measuring method, the time when the signal detected by the pulse signal detecting process exceeds the predetermined threshold is detected. Even in the case of a speaker of slow rising, such as a subwoofer, therefore, it is possible to detect a rising portion in which the amplitude is very low. Consequently, the rising time of the output of the speaker can be correctly detected. When the threshold is adequately set, the true rising time can be detected by capturing the first response, even under circumstances where background noises or indirect sound components have a large energy.
The other sound field measuring method of the invention comprises: a pulse signal generating process of outputting a pulse signal to speakers (4a, 4b, . . . ); a pulse signal detecting process, disposed in an acoustic space where the speakers (4a, 4b, . . . ) are placed, of detecting a pulse signal output from each of the speakers (4a, 4b, . . . ); a rising emphasizing process of emphasizing rising of the signal detected by the pulse signal detecting process; a time detecting process of detecting a time when the signal obtained from the rising emphasizing process exceeds a predetermined threshold; and a calculating process of calculating a time period from a time when the pulse signal is generated by the pulse signal generating process to a time of detection by the time detecting process.
In the sound field measuring method, the time when the signal detected by the pulse signal detecting process exceeds the predetermined threshold is detected. Even in the case of a speaker of slow rising, such as a subwoofer, therefore, it is possible to detect a rising portion in which the amplitude is very low. Consequently, the rising time of the output of the speaker can be correctly detected. When the threshold is adequately set, the true rising time can be detected by capturing the first response, even under circumstances where background noises or indirect sound components have a large energy. Furthermore, the time when the signal which has undergone the process of emphasizing rising of the signal detected is the pulse signal detecting process is detected. Even in the case of a speaker of slow rising, therefore, it is possible to detect a time in the vicinity of the rising of the speaker.
The pulse signal output by the pulse signal generating process may be a signal in which a power is concentrated into a region that is lower in frequency than an impulse signal. In this case, the S/N ratio with respect to background noises in which the level of the low frequency region is usually low can be set to be larger, and hence the rising time of the speaker can be correctly detected even under circumstances where background noises are relatively large.
The pulse signal may be a signal which attenuates with the lapse of time after rising of the pulse signal, or the pulse signal may be an exponential pulse. Alternatively, the pulse signal may be a signal which is obtained by passing an impulse signal through a low-pass filter. The pulse signal may be output by actually passing an impulse signal through a low-pass filter, or a signal which is obtained by passing an impulse signal through a low-pass filter may be stored as data, and a signal which is produced on the basis of the data may be output.
The pulse signal output by the pulse signal generating process may be a signal in which a power is concentrated into a region that is lower in frequency than an impulse signal. The rising emphasizing process may perform a process of substantially flattening a frequency characteristic of the signal which is to be processed by the time detecting process.
In this case, since the frequency characteristic of the signal which is to be processed by the time detecting process is substantially flattened, it is possible to extract the true transmission characteristic, so that measurement can be performed at the same accuracy irrespective of the band used by the speaker.
The pulse signal may be an exponential pulse, and the rising emphasizing process may perform a process of applying differential of first order to the signal detected by the pulse signal detecting process. In this case, in the process of emphasizing the high frequency region and linearizing phase delay between bands, the computational complexity in the rising emphasizing process can be suppressed to a minimum level.
The method may further comprises: a signal delaying process of delaying an audio output signal which is output to the speaker (4a, 4b, . . . ); and a delay time setting process of setting a delay time of the signal delaying process on the basis of the time calculated by the calculating process. In this case, the delay time of the signal delaying process can be set to a desired delay time in accordance with the time calculated by the calculating process, without requiring a cumbersome work.
In order to facilitate understanding of the invention, the reference numerals used in the accompanying drawings are added in the parentheses. However, it is to be understood that the addition of the reference numerals is not intended as restriction of the invention to illustrated embodiments.